The subject invention is generally concerned with a method and article of manufacture of ultra-low friction carbon-based films. More particularly, the invention relates to a carbon containing film grown from a plasma containing about 25-95% hydrogen and about 75-5% of a carbon containing source gas such as methane, acetylene, ethylene, propane and ethane. A plasma activated chemical vapor deposition process is the preferred method but high quality carbon films can also be obtained by magnetron sputtering, ion plating, laser ablation, ion-beam assisted deposition, arc-physical vapor deposition and other vapor deposition processes which take advantage of the use of particular ratios of hydrogen to carbon atoms in the starting gaseous mixture.
A large variety of diamond, diamond-like and amorphous carbon films have been developed for use in applications requiring resistance to mechanical wear, abrasion and corrosive chemical conditions. Some of the carbon-based coatings, such as diamond (hereinafter when used alone means the crystalline form) and amorphous carbon, are currently being evaluated for applications requiring low friction, long wear life, and high resistance to abrasion. Diamond films can be deposited on particular types of substrate materials by a variety of chemical vapor deposition processes at temperature ranging from 700-1000xc2x0 C. Mechanically, these coating are very hard and abrasion resistant; however, they may contain large diamond grains and/or have non-diamond precursor materials between grains, and some of these surfaces can be very rough. When used in machining or sliding wear applications, they cause high frictional losses and severe wear damage on the initial mating surfaces. In addition, diamond can be deposited on only certain substrates due in part to the high substrate temperatures needed. It is also often necessary to etch or polish these diamond films to obtain a smooth surface finish in order to achieve low friction and wear. In addition, the manufacturing process technology for depositing diamond-like carbon is much better understood and developed, making diamond-like carbon films less expensive to manufacture than diamond deposition processes. Unlike most conventional diamond, amorphous carbon or diamond-like carbon films are extremely smooth and have unique mechanical properties, such as high hardness and resistance to corrosion. In general, these coatings are electrically insulating and can be made optically transparent to visible infrared and ultraviolet lights. Adding to their unique mechanical, chemical, electronic, and optical properties is the very low friction and high wear properties of these coatings. Typical friction coefficients are 0.01 to 0.3, depending on test conditions and deposition methods.
Amorphous carbon films can be deposited at temperatures ranging from sub-zero to 200xc2x0 C. and at fairly high deposition rates by a variety of methods, including, for example, ion-beam deposition, DC and RF sputtering, arc-plasma, plasma enhanced chemical-vapor-deposition, and laser ablation. Methane, acetylene, and graphite are typically used as sources for carbon, and structurally the resulting carbon films are amorphous. Within their amorphous structure there are also very-short-range-ordered diamond bonds (characterized by sp3-type tetrahedral bonds) and also graphitic phases (characterized by sp2-type trigonal bonds). Hence, these films can be regarded as degenerate forms of bulk diamond and/or graphite. As a result, the reported tribological performance of diamond and amorphous carbon films differ substantially from one study to another. Certain ones of these coatings can become easily graphitized at elevated temperatures, and their wear properties can degrade.
It is therefore an object of the invention to provide an improved method and article of manufacture of a carbon film.
It is another object of the invention to provide a new method and article of manufacture of a carbon-based film having ultra-low friction coefficients and wear rates.
It is also an object of the invention to provide an improved method and article of manufacture of an amorphous diamond-like carbon film prepared from hydrocarbon and hydrogen gases.
It is a further object of the invention to provide a new method and article of manufacture of a diamond-like carbon film prepared using particular ratios of hydrogen to carbon content in a starting gas to produce ultra-low friction carbon films.
It is yet a further object of the invention to provide an improved method and article of manufacture produced using large amounts of hydrogen compared to the amount of carbon present in a starting gas mixture to form ultra-low friction carbon films.
It is still an additional object of the invention to provide a new method and article of manufacture in which a mixture of hydrogen and carbon containing gas, such as a hydrocarbon, are mixed to produce in a plasma having a carbon to hydrogen atomic molar ratio not more than 0.23, including all hydrogen present in the hydrocarbon as well as H2.
It is an additional object of the invention to provide an improved method and article of manufacture of diamond-like carbon film exhibiting a molecular structure, as characterized by Fourier Transform Infrared (FTIR) Spectroscopy, providing ultra-low friction and wear properties.
It is still another object of the invention to provide a new method and article of manufacture of carbon film with an underlying silicon film, deposited on a substrate, with the film composite exhibiting ultra-low friction and wear properties.
It is also a further object of the invention to provide an improved method and article of manufacture of carbon film disposed on a substrate of one or more of steel, ceramic, plastic, polymers, semiconductors and other solid materials with the carbon film acting to protect the substrate from mechanical wear or chemical corrosion.
These and other objects, features and advantages of the invention will be apparent from the following description of the preferred embodiments and examples, taken in conjunction with the accompanying drawings described below.